The present invention relates to distillation systems for liquid treatment processes. In particular, the present invention relates to distillation systems containing hollow fiber membrane modules for separating distillate fluids from feed solutions in liquid treatment processes.
In recent years, membrane distillation has become increasingly popular in a variety of fluid-treatment applications. The membranes are typically hydrophobic and microporous to keep the feed solution separated from that of the distillate during operation. Hollow fiber membranes are typically employed in tube/shell configurations, where bundles of hollow fiber membranes are arranged along the longitudinal axes of the modules. For membrane distillation, each hollow fiber membrane in the bundle is typically a hydrophobic, microporous membrane having an exterior surface and an inner hollow tubular region. The exterior surfaces of the hollow fiber membranes face a shell side of the module, which is the portion of the module containing the feed solution. The inner hollow tubular regions define a tube side of the module, which provides a conduit for collecting the distillate fluids separated from the feed solution.
During membrane distillation, the feed solution is typically preheated to form a temperature differential across the hollow fiber membranes. This temperature differential creates a vapor pressure differential between the shell side and the tube side of the fibers in the module, which causes a portion of the feed solution to evaporate and the vapor transmits through the hollow fiber membranes. The transmitted vapor then condenses at the internal surface/liquid interface of the membranes on the distillate side, thereby providing the desired distillate fluid. Because the desired distillate fluid is obtained from the membrane separation process, the production rate of the desired distillate fluid is dependent on the separation rate across the hollow fiber membranes. Thus, there is an ongoing need for systems and techniques for increasing the separation rates across hollow fiber membranes.